The characterization of individual molecules has been a scientifically attractive and challenging task for decades, and remains so today. New technological developments have facilitated great progress in our understanding of the structure and behavior of single atoms and molecules in various environments. This book provides an introduction to the most important experimental and theoretical methods for characterizing and imaging single molecules, including scanning tunnelling and atomic force microscopy of molecules at surfaces, fluorescence studies, near-field optical microscopy and Raman spectroscopy. It also elucidates newly discovered properties of single-molecular systems and their relevance to the fast growing field of nanotechnology.